1. Field of the Invention
The present invention relates to a power calibration method and a power calibration apparatus which determine the optimum writing power through writing information for test writing by emitting a laser light to a power calibration area on an optical disc, and reading the written information.
2. Description of the Related Art
When writing information into a recordable (write-once) optical disc (CD-R), the writing power is optimized by performing “test writing” into the power calibration area (hereinafter referred to as “PCA”) beforehand. The process of optimizing the writing power will now be described with reference to FIGS. 8 and 9.
AS shown in FIG. 8, the PCA 81 is divided into a test area 82 and a count area 83. The count area 83 is composed of one hundred count frames (CF01 to CF100), and the test area 82 is composed of one hundred partitions 84 (TA01 to TA100). A partition 84, which is composed of fifteen test frames (TF01 to TF15), is an area used for one power calibration. In prior art, as shown in FIG. 9, the optimization is performed by: writing a predetermined information into each of the fifteen test frames (TF01 to TF15) used for one power calibration, or in one partition 84, through changing the writing power in steps respectively, that is, in fifteen steps total; reading the written information; based on the reproducing signals, selecting the writing power in which the writing condition is the best; and writing information in accordance with the selected writing power.
In Japan as well as in other countries, enormous kinds of optical discs exist, and the recording sensitivity of these optical discs varies. Therefore, it may be difficult to determine the optimum writing power to all those having low recording sensitivity to those having high recording sensitivity from the result of writing and reading information, using the fifteen test frames.
Accordingly, in the prior art, there are some cases which perform the power calibration using a plurality of partitions 84 so as to improve the precision in determining the optimum writing power.
In order to improve the precision in determining the optimum writing power, it is necessary to perform the power calibration for multiple number of times using a plurality of partitions 84 as described above. However, since the PCA 81 only reserves for one hundred time use (that is, having one hundred partitions 84 only), there may be a case that the PCA 81 is run out and the optical disc becomes out of use during a process of writing a plurality of sessions or packet writing.
In the Japanese Patent Laid-Open No.7-34052 and No.10-161734, a technique for saving the PCA is disclosed, in which the power calibration is performed by further dividing each fifteen frame having the smallest area into a plurality of areas.
Although these examples can save the PCA, one of the fifteen frames with the smallest area is further divided into fifteen frames in either case, and the writing power is determined from the result of writing and reading information using the divided fifteen frames, causing only a small number of samples for determining the writing power. Consequently, an error in the optimum writing power may be large.